From: Francesco Ruggiero Organization: CERN X-Mailer: Mozilla 4.72 [en] (Windows NT 5.0; I) X-Accept-Language: en MIME-Version: 1.0 To: Miguel Jimenez , Adriana Rossi , Frank Zimmermann , Daniel Schulte , Gianluigi Arduini Subject: Short summary of our discussion on electron cloud Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear colleagues, I enclose a short summary of our discussion on electron cloud and a list of agreed actions. Ciao Francesco E-cloud meeting with MJ, AR, FR, FZ, DS, and GA ----------------------------------------------- Vacuum pressure might be ~10 times higher than acceptable in ALICE and other LHC experiments. Desired pressure is 10^-9 mbar, while the value estimated with e-cloud increases by 3-4 orders of magnitude and in NEG coated chambers is 10^-8 mbar (pessimistic, since no e-cloud was observed in NEG coated chambers in the SPS). Chris Benvenuti recommends to revise beam and electron gas ionization plus NEG outgassing. SPS experiments in 2003 should measure total number of electrons above 5-10 eV, dependency of scrubbing efficiency on electron energy, position of stripes, and electron energy spectrum. ==> New e-cloud simulations and benchmarking needed. Code bug recently discoverd by FZ and a few others by Giovanni Rumolo at Rutherford: beam kick included twice (not substracted from image current effect), much better agreement with measured radial position of stripes in dipole field. Still bugs in image charge routine for elliptic vs rectangular chamber? It remains also to clarify why simulations do not predict e-cloud threshold with B=0 being higher than with B-field as observed in SPS. New SPS e-cloud diagnostics: - NEG test bench (to test NEG re-cycling and reduced outgassing, effect of multi-layers on SEY, etc.) - cold strip detector (to validate scrubbing in cold conditions) - variable aperture strip detector (for e-cloud in large exp chambers): ==> needs calculation of wake fields/trapped modes at chamber step - COLDEX with 67 mm inner diameter and smaller slots. MD requests: 10-11 days scrubbing run at beginning of May. Prepare program of base and additional measurements in case the scrubbing goes faster than last year. Shall we accelerate to 150 GeV or more? Can we increase beam current or number of bunches for SPS scrubbing? Other important measurements could be kicker heating, effect of orbit bumps, emittance increase in coast over 15-20 minutes. 4 batches may conflict with reduced time for PS fixed target experiments, ISOLDE, NTOF, etc. AGREED ACTIONS: => MJ will send FR his recent informal note and will inform GA about MD requests (e.g. number of batches and cycles for scrubbing). => AR will revise NEG simulations with the help of FZ for ionization. => FZ+DS will continue intensive de-bugging of e-cloud codes, possibly with the help of GSI/Rutherford. => FR will follow-up impedance of cold strip detector and COLDEX, CPU needs/resources (including EU parallel computers) and possibly invite G. Rumolo and/or his smart collaborator at Rutherford for a few days. => MJ will organize meeting with Noel Hilleret et al in 1-2 weeks to discuss 1) SEY modelling before we launch new simulation campaign and 2) back-scattering of photons on saw-tooth structure (as requested by LHC-MAC). He will also send FZ and GA information on strip measurements during last scrubbing run to retrieve beam data. => We will have another meeting in the period 24-28 February to coordinate Chamonix presentations on e-cloud. => Mini-workshop on SPS Scrubbing Run in mid-June? -- E-mail: Francesco.Ruggiero@cern.ch, Location: Building 9/1-008 Address: CERN, A&B Division, CH-1211 Geneva 23, Switzerland Telephone: +41 (22) 767 3726 or 767 5272, TeleFax: +41 (22) 783 0552 WWW: http://wwwslap.cern.ch/~rgo/